Induction of interleukin-1 in articular cartilage by explantation and cutting




To investigate the effect of explantation and fine cutting of articular cartilage upon intracellular inflammatory signaling pathways and expression of interleukin-1 (IL-1).


Cartilage from porcine metacarpophalangeal joints was cultured in serum-free medium. Tissue extracts were examined for ERK activation by phosphorylated–Western blotting, for JNK and p38 MAPK activity by kinase assay, and for IκBα. IL-1α and IL-1β messenger RNA (mRNA) was measured by reverse transcriptase–polymerase chain reaction. IL-1 activity was measured by the induction of serum amyloid A protein in cultured chondrocytes.


All 3 MAPKs (p38, JNK, and ERK) were rapidly activated upon dissection and explantation of the cartilage. IL-1α and IL-1β mRNA was also induced: the speed and magnitude of induction were increased if the explants had been finely cut. IL-1 activity that could be inhibited by IL-1 receptor antagonist or antibodies to IL-1α was found in extracts of explants cultured for 20 hours or lysates of cells isolated from them. This activity was likely due to intracellular proIL-1α that was not secreted. ProIL-1β would not be detected because it is biologically inactive. The mechanism of inflammatory signaling pathway activation underlying the induction of IL-1 is unknown.


Explantation and cutting of articular cartilage activates intracellular inflammatory signaling pathways and induces expression of mRNA for IL-1α and IL-1β. Biologically active IL-1α protein was detectable in cartilage lysates and was probably intracellular proIL-1α. We were unable to show that IL-1 was secreted by chondrocytes.